Contour crafting is a manufacturing process used to fabricate large-scale, three-dimensional structures in a layer-by-layer manner by extruding a flowable material similar to concrete. The flowable material is extruded through an extrusion tip carried by a print head, and deposited in a sequence of paths on a substrate in a plane. The extruded material fuses with previously deposited material, and solidifies upon a decrease in temperature. The position of the print head relative to the substrate is then incremented along a height, perpendicular to the plane, and the process is then repeated to form the three-dimensional structure. The movement of the print head with respect to the substrate is performed under computer control, in accordance with preprogramed depositing paths. The depositing paths are obtained by initially slicing a digital representation of the three-dimensional structure into multiple horizontally sliced two-dimensional layers. Then, for each sliced two-dimensional layer, a path for depositing the flowable material is determined.
One way for implementing contour crafting is using a stationary machine, such as a modified gantry crane. The modified gantry crane is stable, but cumbersome to set up. The crane also imposes limitations on the size of three-dimensional structure that can be manufactured. Another way for implementing contour crafting is using a mobile machine, such as excavator. The excavator may hold a printing tool while it deposits the layers of flowable material. One challenge of using mobile machines for contour crafting is maintaining a high level of accuracy and repeatability of the print head. If the print head deposits layers offset from one another, the stability and strength of the printed structure may be impaired.
U.S. Pat. No. 8,644,964 (the '964 patent) to Hendron et al. discloses a device and a method for controlling movement of a reference point on an end effector coupled to an excavator. The '964 patent indicates that vibration and other factors can alter the location of the reference point when the excavator moves the reference point in a defined path. Accordingly, the '964 patent suggests a device having two closed loop control systems. The first closed loop control system is adapted to determine an actual location of the reference point, and to detect a difference between the actual location and a desired location. The second closed-loop control system is configured to move the reference point from the actual location to the desired location.
Although aiming to provide a controlled movement of a print head coupled to an excavator, the system of the '964 patent is still limited. In particular, the system of the '964 patent does not take into consideration the placement of previously deposited material when adjusting the location of the reference point. Thus, when the location of the print head is at the desired location, there may still be a small deviation with respect to the placement of the previously deposited material. Since these large-scale, three-dimensional structures are achieved using an additive processes, any small deviation may have a cumulative significant effect.
The disclosed system is directed to solving one or more of the problems set forth above and/or other problems of the prior art.